1. Field of the Invention
The present invention relates to an auto-focusing apparatus suitable for a surveying instrument such as an automatic level, a theodolite, a transit, etc., that is provided with a sighting telescope.
2. Description of the Related Art
In recent years various types of surveying instruments provided with a passive AF (auto-focusing) apparatus have been developed. In these types of surveying instruments, the sighting telescopic optical system is provided with a split optical path which branches off from the main optical path. The image of an object (sighting object) formed in the split optical path at a position, optically equivalent to the position at which the focusing plate is placed, is separated into two by a pair of separator lenses to be respectively re-formed onto a pair of sensors. Each photoelectric converting element provided on each sensor converts the received light into an electric charge and accumulates the electric charge. The accumulated electric charges are output in order at every photoelectric conversion element as AF sensor data. A predetermined operation is performed in accordance with the AF sensor data to determine the phase difference between a pair of images respectively formed on the pair of sensors. Furthermore, an object distance or amount of defocus that is necessary for bringing the sighting object into focus is calculated through a predetermined operation in accordance with the determined phase difference. A focusing optical system is driven to bring the sighting object into focus in accordance with the calculated object distance or amount of defocus. In some surveying instruments, if the phase difference cannot be determined, a process in which the pair of sensors are controlled so that each photoelectric converting element thereof converts the received light into an electric charge and accumulates (integrates) the electric charge to obtain AF sensor data while the focusing optical system is driven to move, and subsequently, the phase-difference determining operation is performed in accordance with the obtained AF sensor data, and is repeatedly performed until the phase difference is determined.
The focus detection range (object distance range) of the sighting telescopic optical system of a surveying instrument from an infinite distance to the close-up extremity is very wide, so that the moving range of the focusing optical system is long (approximately 30 mm if the focusing optical system is made up of an concave lens). Therefore, in the phase-difference determining operation performed in accordance with the AF sensor data obtained by performing an integrating operation once, since the object distance range in which the phase difference can be determined is short, the integrating operation and the phase-difference determining operation have to be repeatedly performed many times while the focusing optical system is driven to move. This takes a long time for the sighting object to be brought into focus.
The primary object of the present invention is to provide an auto-focusing apparatus which makes it possible to reduce time taken to bring the sighting object into focus.
To achieve the object mentioned above, according to an aspect of the present invention, an auto-focusing apparatus is provided including a light receiving device having at least one array of photoelectric conversion elements, the light receiving device separating an image of an object formed via an optical system into two separate images to re-form the two separate images on the at least one array of photoelectric conversion elements so as to output two sets of image data, the optical system including a focusing optical system; a driving device which drives the focusing optical system along an optical axis thereof; an operation device which performs a predetermined operation for determining a phase difference between the two separate images while shifting at least part of one of the two sets of image data relative to the other of the two sets of image data; and a controller which limits a range of shifting of the at least part of one of the two sets of image data relative to the other of the two sets of image data in accordance with an amount of movement of the focusing optical system and a moving direction thereof, when the operation device performs the predetermined operation in accordance with the two sets of image data output from the light receiving device while the driving device drives the focusing optical system along the optical axis.
In an embodiment, the controller which does not limit the range when the operation device performs the predetermined operation in accordance with the two sets of image data output from the light receiving device while the driving device does not drive the focusing optical system along the optical axis.
In an embodiment, with reference to a relative position between the two sets of image data at which the two sets of image data for the two separate images are in phase with each other when the optical system is focused on the object, the operation device performs the predetermined operation to determine the phase difference while shifting the at least part of one of the two sets of image data relative to the other of the two sets of image data in a first direction capable of determining a phase difference between the two separate images, which correspond to the two separate images, of an object positioned nearer than the in-focus object, and in a second direction capable of determining a phase difference between two separate images, which correspond to the two separate images, of an object positioned farther than the in-focus object. Preferably, the operation device performs the predetermined operation to determine the phase difference while shifting the at least part of one of the two sets of image data relative to the other of the two sets of image data in steps of one pixel.
In an embodiment, the operation device performs the predetermined operation to determine the phase difference while shifting the at least part of one of the two sets of image data relative to the other of the two sets of image data, with the other of the two sets of image data being stationary, in a first direction capable of determining a phase difference between two separate images, which correspond to the two separate images, of an object at a near distance, and in a second direction capable of determining a phase difference between two separate images, which correspond to the two separate images, of an object at a far distance. Preferably, the operation device performs the predetermined operation to determine the phase difference while shifting the at least part of one of the two sets of image data relative to the other of the two sets of image data in steps of one pixel.
In an embodiment, when the operation device performs the predetermined operation to determine the phase difference while shifting the at least part of one of the two sets of image data relative to the other of the two sets of image data in one of the first direction and the second direction, the operation device limits a first secondary range in the range of shifting of the at least part of one of the two sets of image data relative to the other of the two sets of image data, wherein a phase difference between two separate images, which correspond to the two separate images, of the object at a far distance can be detected in the first secondary range in accordance with an amount of movement of the focusing optical system when the driving device drives the focusing optical system along the optical axis in a direction of bringing the object at a near distance into focus; the operation device limits a second secondary range in the range of shifting of the at least part of one of the two sets of image data relative to the other of the two sets of image data, wherein a phase difference between two separate images, which correspond to the two separate images, of the near distance object can be detected in the second secondary range in accordance with an amount of movement of the focusing optical system when the driving device drives the focusing optical system along the optical axis in a direction of bringing the far distance object into focus; and the operation device performs the predetermined operation to determine the phase difference between the two separate images while shifting the at least part of one of the two sets of image data relative to the other of the two sets of image data within one of the first secondary range and the second secondary range that is not limited by the operation device.
In an embodiment, the operation device performs an operation for calculating the difference between two image data of two adjacent pixels on every pair of two adjacent pixels of each of the two sets of image data and further calculates the sum of the absolute values of the calculated differences while shifting the at least part of one of the two sets of image data relative to the other of the two sets of image data in pixels. The operation device performs a correlation operation in accordance with the calculated the sum of the absolute values to determine the phase difference, and the operation device determines the amount of movement of the focusing optical system and the moving direction thereof in accordance with the determined phase difference.
In an embodiment, the shifting range limited by the controller corresponds to a part of an overlapping portion between a first shifting range before the focusing lens group is driven by the driving device, and a second shifting range after the focusing lens group is driven by the driving device. Preferably, the shifting range limited by the controller corresponds to at least part of the overlapping portion, and wherein a degree of reliability of the phase difference determined by the operation device before the focusing optical system is driven by the driving device is considered high in the at least part of the overlapping portion.
In an embodiment, the shifting range limited by the controller corresponds to an overlapping portion between a first shifting range before the focusing lens group is driven by the driving device, and a second shifting range after the focusing lens group is driven by the driving device. Preferably, the shifting range limited by the controller corresponds to at least part of the overlapping portion, and wherein a degree of reliability of the phase difference determined by the operation device before the focusing optical system is driven by the driving device is considered high in the at least part of the overlapping portion.
Preferably, the auto-focusing apparatus is incorporated in a surveying instrument.
According to another aspect of the present invention, a surveying instrument is provided including a telescopic optical system having a main optical path and a split optical path which branches off from the main optical path, the telescopic optical system including a focusing lens group guided along an optical axis thereof; a focus detector having a passive AF sensor positioned so that light traveling from the main optical path to the split optical path is incident on the focus detector, the passive AF sensor including at least one array of photoelectric conversion elements, the focus detector separating an image of an object formed via the telescopic optical system into two separate images to re-form the two separate images on the at least one array of photoelectric conversion elements so as to output two sets of image data; a driving device which drives the focusing lens group along the optical axis for focusing; an operation device which performs a predetermined operation for determining a phase difference between the two separate images while shifting at least part of one of the two sets of image data relative to the other of the two sets of image data; and a controller which limits a range of shifting of the at least part of one of the two sets of image data relative to the other of the two sets of image data in accordance with an amount of movement of the focusing lens group and a moving direction thereof when the operation device performs the predetermined operation in accordance with the two sets of image data output from the focus detector while the driving device drives the focusing lens group system along the optical axis.
According to another aspect of the present invention, an auto-focusing apparatus is provided including a light receiving device including at least one array of photoelectric conversion elements and separating an image of an object formed via an optical system into two separate images to re-form the two separate images on the at least one array of photoelectric conversion elements so as to output two sets of image data, the optical system including a focusing optical system; a driving device which drives the focusing optical system along an optical axis thereof; a detecting device which detects a phase difference between the two separate images re-formed on the array of photoelectric conversion elements by the two sets of image data; and a controller which limits a area of the array of photoelectric conversion elements to detect the phase difference in accordance with an amount of movement of the focusing optical system and a moving direction thereof when the detection device performs the detection operation in accordance with the two sets of image data output from the array of photoelectric conversion elements while the driving device drives the focusing optical system along the optical axis.
In an embodiment, the controller which does not change the area of the array of photoelectric elements when the detecting device performs the operation in accordance with the two sets of image data output from the light receiving device while the driving device does not drive the focusing optical system along the optical axis.
In an embodiment, the controller changes the area of the array of photoelectric elements to a larger area in accordance with a larger amount of movement of the focusing optical system; and a predetermined calculation process is performed to obtain a phase difference from a reference pixel position to a position subtracted from a predetermined maximum data shifting amount, only by a data shifting amount, in a direction depending on a moving direction of the focusing lens group, to obtain a calculation starting pixel position.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 11-276575 (filed on Sep. 29, 1999) which is expressly incorporated herein by reference in its entirety.